$$ The \quad original\quad list \quad is :a_1\quad a_2 \quad a_3 \quad 40 $$

$$ The \quad new \quad list \quad is :a_1\quad a_2 \quad a_3 \quad 48 $$

We know that,

$$ A=\frac{sum}{n_0} $$

$$ A=\frac{328+48}{4} $$

$$ A=94 $$